In this project, we will test the hypothesis that combined therapy with DHEA and estrogen/progestin will enhance bone mass in patients with AN through anabolic and antiosteolytic mechanisms. We will test the hypothesis that 18 months of DHEA + HRT will increase bone mineral density (BMD) and markers of bone formation, while decreasing bone resorption markers in these patients. The proposed study will examine whether restoring normal levels of DHEA and estrogen in these young women will increase bone mass during a critical period for bone accretion. The study will also examine whether DHEA's anabolic effects on bone are mediated through the skeletal IGF-I regulatory system. Using cross-sectional analyses of dual energy x-ray absorptiometry (DXA) data, we will also measure indices of bone structural geometry to determine if mechanical strength is compromised in these young women, and if strength is restored in response to combined anabolic/antiresorptive therapy.